This invention relates to a level-indicating device, provided with a mounting by means of which the device may be mounted in the wall of a bin, tank or other container, a drive motor mounted in said mounting to be freely rotatable about the axis thereof, an oscillating transmission assembly connected to said motor with an output shaft and a vane mounted on said shaft whereby the drive motor is provided with switch means to generate a signal and to cut the motor off when the vane plate meets a resistance.
A known level indicator of the above-defined kind is provided with a continuously-rotating vane, whereby a friction clutch is arranged between the output shaft of the motor and the vane shaft which will slip whenever the vane meets a predetermined too-high resistance. In this arrangement the motor is suspended by springs and rotates within bearings. When the vane meets a resistance, the motor housing will rotate against the spring action and operate the switch means to generate a signal and cut the motor off. As soon as the resistance stops acting on the vane, the motor housing and hence the vane will return under the action of the spring force thereon to the original position whereby the switch means are released and the motor will rotate again together with the vane.
This known device requires due to the continuously-rotating vane, a dynamic seal between the vane shaft and the container frame or wall. Known seals are, for example, oil-return rings, packing bushings, mechanical seals, or some other dynamic seal. If desired, such a seal may be further protected and improved by providing a protecting gas or liquid.